If you have a fresh Ubuntu install, you may not be able to access Windows Shares properly. You might find that Windows will reject any attempt to access a Share, not with an error, but instead with the same credentials prompt over and over again, even though the credentials are correct.
On the Windows machine, make sure that full rights are granted for Everyone which includes read and write access. Just checking Share on a folder isn’t enough – Ubuntu sharing requires full rights.
Another thing to check is that there is a password. Ubuntu won’t allow sharing if there is no password set on the Windows side. In short – if the account that owns the share does not have a password, Ubuntu won’t like it.
Samba is probably what is being used to share files. There might be a couple of Samba packages but the one that is needed most for Linux to Windows sharing is the the sbmfs package.
sudo apt-get install smbfs.
Now try to access the Windows Share again and the odds are you’ll get through this time.